Turning angle detecting device and electric power steering device

ABSTRACT

A turning angle detecting device includes: a first storage unit configured to store a turning angle neutral point correction value being a difference between a median of the turning angles at respective limits in right and left steering and the turning angle in a straight traveling state; a second storage unit configured to store an initial position of a movable portion of an actuator of a wheel turning mechanism in the straight traveling state; a first turning angle calculating unit configured to calculate a first turning angle with respect to the median of the turning angles at the respective limits based on a detection value of a position of the movable portion; and a second turning angle calculating unit configured to calculate a second turning angle based on the detection value, the turning angle neutral point correction value, the initial position and the first turning angle.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/JP2022/004505 filed Feb. 4, 2022, claiming priority based onJapanese Patent Application No. 2021-071912 filed Apr. 21, 2021.

TECHNICAL FIELD

The present invention relates to a turning angle detecting device and anelectric power steering device.

BACKGROUND ART

PTL 1 below describes a technology that detects turning angles atrespective limits when a steering wheel is steered right and left,respectively, sets a median thereof as a turning angle neutral point,and obtains a turning angle with respect to the neutral point.

In the following description, turning angles at limits in right and leftsteering may be described as “rack end turning angles”. For example,when assuming that a turning angle value on a right side from a neutralposition is positive and a turning angle value on a left side therefromis negative, the rack end turning angle in right steering is a maximumturning angle when the steering wheel is steered to a rightward limit,and the rack end turning angle in left steering is a minimum turningangle when the steering wheel is steered to a leftward limit.

CITATION LIST Patent Literature

PTL 1: JP Pat. No. 4323402 B2

SUMMARY OF INVENTION Technical Problem

However, the median of the left and right rack end turning angles doesnot necessarily coincide with a turning angle when a vehicle is in astraight traveling state, and also an error occurs in detection of therack end turning angles. Therefore, the technology described in PTL 1cannot accurately calculate a turning angle with respect to the turningangle when the vehicle is traveling straight.

The present invention has been made in view of the problem describedabove. It is an object of the present invention to calculate, with highaccuracy, a turning angle with respect to a turning angle when a vehicleis traveling straight.

Solution to Problem

In order to achieve the above-described object, according to an aspectof the present invention, there is provided a turning angle detectingdevice including: a position detecting unit configured to detect aturning angle of a wheel turning mechanism; an actuator configured todrive the wheel turning mechanism; a first storage unit configured tostore a turning angle neutral point correction value being a differencebetween a median of the turning angles at respective limits in rightsteering and left steering and the turning angle when a vehicle istraveling straight; a second storage unit configured to store anactuator initial position being a position of a movable portion of theactuator when the vehicle is traveling straight; an actuator positiondetecting unit configured to detect the position of the movable portionof the actuator as a first actuator position; a first turning anglecalculating unit configured to calculate, as a first turning angle, theturning angle of the wheel turning mechanism with respect to the medianof the turning angles at the respective limits in the right steering andthe left steering on a basis of the first actuator position; and asecond turning angle calculating unit configured to calculate a secondturning angle with respect to the turning angle of the wheel turningmechanism when the vehicle is traveling straight on a basis of the firstactuator position, the turning angle neutral point correction value, theactuator initial position, and the first turning angle.

In order to achieve the above-described object, according to anotheraspect of the present invention, there is provided an electric powersteering device including the turning angle detecting device describedabove, wherein the actuator is driven on a basis of the second turningangle to apply a turning assist force to the wheel turning mechanism.

Advantageous Effects of Invention

According to the present invention, a highly accurate calculation can bemade for a turning angle with respect to a turning angle when a vehicleis traveling straight.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram illustrating an outline of an exampleof an electric power steering device of an embodiment;

FIG. 2 is a block diagram illustrating an example of a functionalconfiguration of a turning angle detecting unit illustrated in FIG. 1 ;

FIGS. 3A to 3C are illustrative diagrams of an example of a turningangle detection method of an embodiment;

FIG. 4A is a flowchart of an example of an initial setting process, andFIG. 4B is a flowchart of an example of a turning angle informationrestoration process; and

FIGS. 5A and 5B are illustrative diagrams of an example of turning angledetection methods of modifications.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described in detail withreference to the drawings. Note that the embodiments of the presentinvention to be described below indicate devices and methods to embodythe technical idea of the present invention by way of example, and thetechnical idea of the present invention does not limit the constitution,arrangements, and the like of the constituent components to thosedescribed below. The technical idea of the present invention can besubjected to a variety of alterations within the technical scopeprescribed by the claims described in CLAIMS.

(Configuration)

FIG. 1 is a configuration diagram illustrating an outline of an exampleof an electric power steering device of an embodiment. Column shafts(steering shafts) 2 i and 2 o of a steering wheel (steering handle) 1are connected to steered wheels 8L and 8R via a reduction gear (wormgear) 3 constituting a speed reduction mechanism, an intermediate shaft4, a pinion rack mechanism 5, and tie rods 6 a and 6 b, and further viahub units 7 a and 7 b.

The column input shaft 2 i and the column output shaft 2 o are connectedby a torsion bar (not illustrated) that twists due to a rotation angledeviation between the column input shaft 2 i and the column output shaft2 o.

The intermediate shat 4 includes a shaft member 4 c and universal joints4 a and 4 b attached to both ends of the shaft member 4 c. The universaljoint 4 a is connected to the column output shaft 2 o, and the universaljoint 4 b is connected to the pinion rack mechanism 5.

The pinion rack mechanism 5 includes a pinion 5 a connected to a pinionshaft to which steering force is transmitted from the universal joint 4b and a rack 5 b engaging with the pinion 5 a, and converts a rotationalmotion transmitted to the pinion 5 a into a translational motion in avehicle width direction by the rack 5 b.

The steering shafts 2 (column shafts 2 i and 2 o) are provided with atorque sensor 10 that detects a steering torque Th.

Additionally, a motor 20 that assists a steering force of the steeringwheel 1 is connected to the column output shaft 2 o via the reductiongear 3. A rotation shaft of the motor 20 is provided with a rotationangle sensor 21 that detects a mechanical angle θm of the rotationshaft. The mechanical angle θm is an example of a “first actuatorposition” described in the claims.

The amount of rotation of the column output shaft 2 o is obtained bydividing the amount of rotation of the rotation shaft of the motor 20 bya reduction ratio R of the reduction gear 3. A controller 30 calculates,as a turning angle θt, a rotation angle of the column output shaft 2 oobtained by dividing the mechanical angle θm by reduction ratio R of thereduction gear 3.

Note that the motor 20 is an example of an “actuator” described in theclaims. The reduction ratio R of the reduction gear 3 is an example of a“conversion coefficient” described in the claims. In addition, theactuator in the present invention is not limited to a motor, and variouskinds of actuators can be used.

Electrical power from a battery 13 is supplied to the controller 30,which controls an electric power steering (EPS) device, and also anignition key signal is input to the controller 30 via an ignition (IGN)key 11.

The controller 30 calculates a current command value of an assistcontrol command on the basis of the steering torque Th detected by thetorque sensor 10, a vehicle speed Vh detected by a vehicle speed sensor12, and the turning angle θt calculated from the mechanical angle θm ofthe motor 20, and controls current to be supplied to the motor 20 by avoltage control command value Vref obtained by subjecting the currentcommand value to compensation or the like.

The controller 30 may include, for example, a computer including aprocessor and peripheral components such as a storage device. Theprocessor may be, for example, a central processing unit (CPU) or amicro-processing unit (MPU).

The storage device may include any of a semiconductor storage device, amagnetic storage device, and an optical storage device. The storagedevice may include register, cache memory and memories, such as readonly memory (ROM) and random access memory (RAM) used as primary storagedevices.

Functions of the controller 30 described below are achieved by, forexample, causing the processor of the controller 30 to execute acomputer program stored in the storage device.

Note that the controller 30 may be formed by dedicated hardware forexecuting each information processing described below.

For example, the controller 30 may include a functional logic circuitthat is set in a general-purpose semiconductor integrated circuit. Forexample, the controller 30 may include a programmable logic device (PLD)such as a field-programmable gate array (FPGA), or the like.

A function of the controller 30 to detect the turning angle θt of awheel turning mechanism is described below. As described above, thecontroller 30 calculates, as the turning angle θt, the rotation angle ofthe column output shaft 2 o obtained by dividing the mechanical angle θmof the rotation shaft of the motor 20 by the reduction ratio R of thereduction gear 3.

Here, the rotation shaft of the motor 20 is connected to the columnoutput shaft 2 o via the reduction gear 3. Therefore, the mechanicalangle θm of the motor 20 varies more than 360 degrees, which is an angleper rotation, during a time in which the wheel turning mechanism isturned from a neutral position to a rightward or leftward limit.Accordingly, the turning angle θt of the wheel turning mechanism cannotbe determined uniquely from the mechanical angle θm of the motor 20.

Thus, the controller 30 calculates the turning angle θt by holdingturning angle information on the turning angle θt and updating it as themechanical angle θm changes.

While the ignition key 11 is off, the controller 30 counts the number ofrotations of the rotation shaft of the motor 20 instead of detecting themechanical angle θm. For example, the controller 30 counts the number ofrotations per ¼ rotation (i.e., for one quadrant unit) of the rotationshaft of the motor 20.

When the ignition key 11 is switched from off to on, a rotation angle(360×n+θm) of the rotation shaft in an angular range over a plurality ofrotations is calculated on the basis of a number n of rotations countedup to that point in time and the mechanical angle θm detected at thattime, and is divided by the reduction ratio R to obtain the turningangle θt.

However, for various reasons, the turning angle information may be lost.For example, removing the battery from a vehicle in order to avoidbattery drain when transporting the vehicle over a long period of timeresults in loss of the turning angle information. When the turning angleinformation is lost, the turning angle θt is unknown only from themechanical angle θm of the motor 20.

In such a case, detecting left and right rack end turning angles andcalculating a median of the rack end turning angles allows for obtainingof a neutral position of the wheel turning mechanism.

However, the median of the left and right rack end turning angles doesnot necessarily coincide with a turning angle when the vehicle istraveling straight. Therefore, even when a turning angle at which themedian of the rack end turning angles is the neutral position iscalculated, it is not at a neutral position when the vehicle istraveling straight. In other words, it is not a turning angle withrespect to the turning angle when the vehicle is traveling straight.Additionally, an error also occurs when detecting the rack end turningangles, so that the error reduces accuracy.

Thus, the controller 30 of the embodiment includes a turning angledetecting unit 31 that calculates a turning angle with respect to aturning angle when a vehicle is traveling straight.

The turning angle detecting unit 31 stores in advance a turning angleneutral point correction value Δθt, which is a difference between amedian of left and right rack end turning angles and a turning anglewhen the vehicle is traveling straight. In addition, turning angledetecting unit 31 also stores in advance a motor initial position θm0,which is the mechanical angle θm of the rotation shaft of the motor 20detected by the rotation angle sensor 21 when the vehicle is travelingstraight. The motor initial position θm0 is an example of an “actuatorinitial position” described in the claims.

The turning angle detecting unit 31 corrects a turning angle withrespect to the median of the left and right rack end turning angles onthe basis of the turning angle neutral point correction value Δθt andthe motor initial position θm0, thereby allowing for a highly accuratecalculation of a turning angle with respect to the turning angle whenthe vehicle is traveling straight.

FIG. 2 is a block diagram of an example of a functional configuration ofthe turning angle detecting unit 31. The turning angle detecting unit 31includes a first turning angle calculating unit 32, a correctioninformation generating unit 33, a storage unit 34, and a second turningangle calculating unit 35.

The first turning angle calculating unit 32 calculates a turning angleθt1 of the wheel turning mechanism with respect to the median of theleft and right rack end turning angles. In other words, the firstturning angle calculating unit 32 calculates such a turning angle θt1that the median of the left and right rack end turning angles is theneutral position. The turning angle θt1 is an example of a “firstturning angle” described in the claims.

Hereinafter, the median of the left and right rack end turning anglesmay be described as “L2L midpoint position θLn”.

For example, the first turning angle calculating unit 32 detectsrespective left and right rack end turning angles using any giventurning angle θa (for example, a turning angle when power is turned onbefore storing turning angle information) as a reference angle.

The mechanical angle θm of the rotation shaft of the motor 20 varies by360 degrees or more during steering from one limit of right steering andleft steering to the other limit thereof. Therefore, the first turningangle calculating unit 32 may count the number n of rotations of therotation shaft and calculate each angle of the rotation shaft when thelimits of the left and right steering are reached as a rotation angle(360×n+θm) in an angular range over a plurality of rotations. Eachrotation angle is divided by the reduction ratio R to calculate left andright rack end turning angles.

The first turning angle calculating unit 32 obtains the median of theabove rack end turning angles, sets it as the L2L midpoint position θLn,and corrects a turning angle detected with respect to the any giventurning angle θa by the L2L midpoint position θLn (for example, bysubtracting the L2L midpoint position θLn) to calculate the turningangle θt1 with respect to the L2L midpoint position θLn.

The correction information generating unit 33 generates, as the turningangle neutral point correction value Δθt, a difference between the L2Lmidpoint position θLn and the turning angle when the vehicle istraveling straight, and stores it in the storage unit 34. Additionally,the correction information generating unit 33 stores the mechanicalangle θm when the vehicle is traveling straight in the storage unit 34as the motor initial position θm0. The storage unit 34 is an example ofa “first storage unit”, a “second storage unit”, and a “third storageunit” described in the claims.

For example, at the time of factory shipment or the like, the correctioninformation generating unit 33 may generate the turning angle neutralpoint correction value Δθt and the motor initial position θm0 and storethem in the storage unit 34.

For example, the correction information generating unit 33 stores, asthe turning angle neutral point correction value Δθt, a sign-reversedvalue (−θt1) of the output θt1 of the first turning angle calculatingunit 32 when the vehicle is traveling straight in the storage unit 34.

The second turning angle calculating unit 35 corrects the turning angleθt1 on the basis of the mechanical angle θm, the turning angle neutralpoint correction value Δθt, and the motor initial position θm0 tocalculate a corrected turning angle θt2 with respect to the turningangle of the wheel turning mechanism when the vehicle is travelingstraight. The corrected turning angle θt2 is an example of a “secondturning angle” described in the claims.

The second turning angle calculating unit 35 calculates a turning angleθnt with respect to a point where the L2L midpoint position θLn has beencorrected by the turning angle neutral point correction value Δθt.Hereinafter, the turning angle θnt with respect to the point where theL2L midpoint position θLn has been corrected by the turning angleneutral point correction value Δθt is described as “L2L midpoint turningangle θnt”. For example, the second turning angle calculating unit 35may calculate the L2L midpoint turning angle θnt=θt1−Δθt by subtractingthe turning angle neutral point correction value Δθt from the turningangle θt1. The L2L midpoint turning angle θnt is an example of a “thirdturning angle” described in the claims.

The second turning angle calculating unit 35 converts the L2L midpointturning angle θnt to a mechanical angle θnm. Hereinafter, the mechanicalangle θnm is described as “L2L mechanical angle θnm”.

Specifically, the second turning angle calculating unit 35 multipliesthe L2L midpoint turning angle θnt by the reduction ratio R to covertthe L2L midpoint turning angle θnt to a mechanical angle scale.Hereinafter, the L2L midpoint turning angle (θnt×R) converted to themechanical angle scale is described as “converted L2L midpoint turningangle θntc”.

The second turning angle calculating unit 35 calculates, as the L2Lmechanical angle θnm, a remainder mod(θntc, 360) of the converted L2Lmidpoint turning angle θntc divided by 360 degrees, which is an amountof angular change per rotation. The L2L mechanical angle θnm is anexample of a “third actuator position” described in the claims.

Additionally, the second turning angle calculating unit 35 corrects themechanical angle θm detected by the rotation angle sensor 21 by themotor initial position θm0 to calculate a mechanical angle θm2=θm−θm0with respect to the motor initial position θm0. Hereinafter, themechanical angle θm2 is described as “second motor mechanical angleθm2”.

In FIGS. 3A to 3C, dash-dot-dash lines indicate the converted L2Lmidpoint turning angle θntc, solid lines indicate the L2L mechanicalangle θnm, and dashed lines indicate the second motor mechanical angleθm2.

On the basis of a value of a difference (θnm−θm2) between the L2Lmechanical angle θnm and the second motor mechanical angle θm2, thesecond turning angle calculating unit 35 calculates a motor positiondifference Δθm as below. The motor position difference Δθm is an exampleof an “actuator position difference” described in the claims.

(1) When the difference (θnm−θm2)≥(−180) degrees and the difference(θnm−θm2)≥(180) degrees, the difference (θnm−θm2) is set as the motorposition difference Δθm as it is, as illustrated in an arrow view 40 inFIG. 3A.

(2) When the difference (θnm−θm2)≤(−180) degrees, a sum of thedifference (θnm−θm2) plus 360 degrees is set as the motor positiondifference Δθm, as illustrated in an arrow view 41 in FIG. 3B.

(3) When the difference (θnm−θm2)>180 degrees, a difference of thedifference (θnm−θm2) minus 360 degrees is set as the motor positiondifference Δθm, as illustrated in an arrow view 42 in FIG. 3C.

In FIGS. 3A to 3C, dash-dot-dot-dash lines indicate an angle θstcobtained by multiplying a turning angle with respect to the turningangle when the vehicle is traveling straight by the reduction ratio R toconvert the product to a mechanical angle scale. Hereinafter, the angleθstc is described as “converted straight travel midpoint turning angleθstc”.

As can be seen from FIGS. 3A to 3C, by subtracting the motor positiondifference Δθm from the converted L2L midpoint turning angle θntc, theconverted L2L midpoint turning angle θntc can be corrected to theconverted straight travel midpoint turning angle θstc. Dividing theconverted straight travel midpoint turning angle θstc by the reductionratio R allows for calculation of the turning angle with respect to theturning angle when the vehicle is traveling straight.

Here, L2L midpoint turning angle θnt=(converted L2L midpoint turningangle θntc/reduction ratio R). Therefore, the second turning anglecalculating unit 35 calculates, as the corrected turning angle θt2, adifference (θnt−Δθm/R) obtained by subtracting a result (Δθm/R) of themotor position difference Δθm divided by the reduction ratio R from theL2L midpoint turning angle θnt.

This allows the second turning angle calculating unit 35 to calculatethe corrected turning angle θt2 as the turning angle with respect to theturning angle when the vehicle is traveling straight when the following(condition 1) and (condition 2) are satisfied.

(Condition 1): there is no change due to parts replacement or the likein a mechanical unit mounted with the motor 20 from the time of storageof the turning angle neutral point correction value Δθt and the motorinitial position θm0 (for example, the time of factory shipment) to thetime of calculation of the corrected turning angle θt2.

(Condition 2): An error between the L2L midpoint position θLn used whenstoring the turning angle neutral point correction value Δθt and the L2Lmidpoint position θLn used when calculating the corrected turning angleθt2 is less than a mechanical angle of 180 degrees.

(Operation)

Next, an example of a method for detecting a turning angle of anembodiment is described with reference to FIGS. 4A and 4B. FIG. 4A is aflowchart of an example of an initial setting process for generating theturning angle neutral point correction value Δθt and the motor initialposition θm0 and storing them in the storage unit 34.

At step S1, the first turning angle calculating unit 32 detectsrespective left and right rack end turning angles and detects a medianthereof as the L2L midpoint position θLn.

At step S2, the correction information generating unit 33 generates adifference between the L2L midpoint position θLn and the turning anglewhen the vehicle is traveling straight as the turning angle neutralpoint correction value Δθt, and stores the difference in the storageunit 34.

At step S3, the correction information generating unit 33 stores themechanical angle θm when the vehicle is traveling straight in thestorage unit 34 as the motor initial position θm0.

Then, the initial setting process is ended.

FIG. 4B is a flowchart of an example of a turning angle informationrestoration process for calculating the corrected turning angle θt2.This process is performed when the battery is reconnected.

At step S10, the second turning angle calculating unit 35 reads theturning angle neutral point correction value Δθt and the motor initialposition θm0 from the storage unit 34.

At step S11, the first turning angle calculating unit 32 detectsrespective left and right rack end turning angles and detects a medianthereof as the L2L midpoint position θLn.

At step S12, the first turning angle calculating unit 32 calculates theturning angle θt1 with respect to the L2L midpoint position θLn.

At step S13, the second turning angle calculating unit 35 subtracts theturning angle neutral point correction value Δθt from the turning angleθt1 to calculate the L2L midpoint turning angle θnt.

At step S14, the second turning angle calculating unit 35 corrects themechanical angle θm detected by the rotation angle sensor 21 by themotor initial position θm0 to calculate the second motor mechanicalangle θm2 with respect to the motor initial position θm0.

At step S15, the second turning angle calculating unit 35 converts theL2L midpoint turning angle θnt to the motor mechanical angle. Then, thesecond turning angle calculating unit 35 calculates the motor positiondifference Δθm on the basis of a value of the difference (θnm-θm2)between the L2L mechanical angle θnm and the second motor mechanicalangle θm2.

At step S16, the second turning angle calculating unit 35 subtracts theresult (Δθm/R) of the motor position difference Δθm divided by thereduction ratio R from the L2L midpoint turning angle θnt to calculatethe corrected turning angle θt2.

Then, the turning angle information restoration process is ended.

Effects of Embodiment

(1) The rotation angle sensor 21 and the first turning angle calculatingunit 32 detect a turning angle of the wheel turning mechanism. Thecorrection information generating unit 33 stores, in the storage unit34, the turning angle neutral point correction value Δθt, which is thedifference between the median of the turning angles at respective limitsin right steering and left steering and the turning angle when thevehicle is traveling straight, and the motor initial position θm0, whichis the angle of the rotation shaft of the motor 20 when the vehicle istraveling straight. The rotation sensor 21 detects the mechanical angleθm of the rotation shaft of the motor 20. On the basis of the mechanicalangle θm, the first turning angle calculating unit 32 calculates theturning angle θt1 of the wheel turning mechanism with respect to themedian of the turning angles at the respective limits in the rightsteering and the left steering. The second turning angle calculatingunit 35 calculates the corrected turning angle θt2 with respect to theturning angle of the wheel turning mechanism when the vehicle istraveling straight on the basis of the mechanical angle θm, the turningangle neutral point correction value Δθt, the motor initial positionθm0, and the turning angle θt1.

As a result, even when turning angle information is lost, a calculationcan be made for the corrected turning angle θt2 with respect to theturning angle of the wheel turning mechanism when the vehicle istraveling straight.

Additionally, even when an error occurs in the detection of the rack endturning angles, the corrected turning angle θt2 can be calculated withhigh accuracy without including such an error.

(2) The second turning angle calculating unit 35 may calculate thesecond motor mechanical angle θm2, which is the mechanical angle of therotation shaft of the motor 20 with respect to the motor initialposition θm0, on the basis of the mechanical angle θm and the motorinitial position θm0, and may calculate the corrected turning angle θt2on the basis of the L2L midpoint turning angle θnt obtained bycorrecting the turning angle θt1 by the turning angle neutral pointcorrection value Δθt and the second motor mechanical angle θm2.

By correcting the turning angle θt1 by the turning angle neutral pointcorrection value Δθt before correcting on the basis of the second motormechanical angle θm2, correction can be made on the basis of the secondmotor mechanical angle θm2 even when the turning angle θt1 is 180degrees or more away from the turning angle with respect to the turningangle of the wheel turning mechanism when the vehicle is travelingstraight.

(3) The second turning angle calculating unit 35 may calculate thecorrected turning angle θt2 by calculating the motor position differenceΔθm, which is the difference between the L2L mechanical angle θnmcorresponding to the L2L midpoint turning angle θnt and the second motormechanical angle θm2, and correcting the L2L midpoint turning angle θnton the basis of the value (Δθm/R) obtained by dividing the motorposition difference Δθm by the reduction ratio R.

This allows for calculation of the corrected turning angle θt2 on thebasis of the L2L midpoint turning angle θnt and the second motormechanical angle θm2.

(4) The second turning angle calculating unit may calculate, as the L2Lmechanical angle θnm, the remainder mod (θnt×R, 360) of the product(θnt×R) of the L2L midpoint turning angle θnt and the reduction ratio Rdivided by 360 degrees.

This allows for calculation of the L2L mechanical angle θnm for use inthe calculation of the motor position difference Δθm.

Modification 1

The above embodiment is an example of the method for calculating thecorrected turning angle θt2. The corrected turning angle θt2 can becalculated by various methods on the basis of the mechanical angle θm,the turning angle neutral point correction value Δθt, the motor initialposition θm0, and the first turning angle θt1. The following is adescription of several modifications.

The second turning angle calculating unit 35 may calculate a difference(θntc−θm2) of the second motor mechanical angle θm2 subtracted from thecorrected L2L midpoint turning angle θntc, which is the product of theL2L midpoint turning angle θnt and the reduction ratio R, and maycalculate the motor position difference Δθm on the basis of a remaindermod(θntc−θm2, 360) of the difference (θntc −θm2) divided by 360 degrees.

Then, as in FIG. 5A, when mod(θntc−θm2, 360) 180 degrees, the mod(θntc−θm2, 360) is set as the motor position difference Δθm.

On the other hand, as in FIG. 5B, when mod(θntc−θm2, 360)>180 degrees,the mod(θntc−θm2, 360)−360 degrees is set as the motor positiondifference Δθm.

Even setting the motor position difference Δθm in this way allows forcalculation of the corrected turning angle θt2.

Modification 2

The correction information generating unit 33 may calculate a difference(Δθt×R−θm0) of the motor initial position θm0 subtracted from theproduct (Δθt×R) of the turning angle neutral point correction value Δθtand the reduction ratio R, and may store it as a correction amountdifference (Δθt×R−θm0).

The second turning angle calculating unit 35 may calculate a value (θt1×R−(Δθt×R−θm0)−θm) of the correction amount difference (Δθt×R−)θm0 andthe mechanical angle θm subtracted from a product of the first turningangle θt1 and the reduction ratio R.

The value (θt1× R−(Δθt×R−θm0)−θm) calculated in this way can besummarized into (θt1−Δθt)×R−(θm−θm0)=(θntc−θm2), which is equal to thedifference (θntc−θm2) in Modification 1.

Even calculating the difference (θntc−θm2) in this way allows forcalculation of the corrected turning angle θt2.

Modification 3

A correction amount for correcting the L2L midpoint turning angle θntmay be determined on the basis of a difference (θnt−θm2/R) obtained bysubtracting a value θm2/R of the second motor mechanical angle θm2divided by the reduction ratio R to be converted to the scale of arotation angle of the column shaft 2 o from the L2L midpoint turningangle θnt.

For example, the difference (θnt−θm2/R) may be varied by varying themechanical angle θm by steering the steering wheel, the difference(θnt−θm2/R) with the smallest absolute value may be set as thecorrection amount, and the L2L midpoint turning angle θnt may becorrected by the correction amount set in this way to calculate thecorrected turning angle θt2.

This method also allows for calculation of the corrected turning angleθt2.

Modification 4

The turning angle θt may be calculated on the basis of a rotation angledetected by a turning angle sensor mounted on the column input shaft 2 iside or the column output shaft 2 o side.

REFERENCE SIGNS LIST

-   -   1: Steering wheel    -   2 i: Column input shaft    -   2 o: Column output shaft    -   3: Reduction gear    -   4: Intermediate shaft    -   4 a, 4 b: Universal joint    -   4 c: Shaft member    -   5: Pinion rack mechanism    -   5 a: Pinion    -   5 b: Rack    -   6 a, 6 b: Tie rod    -   7 a, 7 b: Hub unit    -   8L, 8R: Steered wheel    -   10: Torque sensor    -   11: Ignition key    -   12: Vehicle speed sensor    -   13: Battery    -   20: Motor    -   21: Rotation angle sensor    -   30: Controller    -   31: Turning angle detecting unit    -   32: First turning angle calculating unit    -   33: Correction information generating unit    -   34: Storage unit    -   35: Second turning angle calculating unit

The invention claimed is:
 1. A turning angle detecting devicecomprising: a position detecting unit configured to detect a turningangle of a wheel turning mechanism; an actuator configured to drive thewheel turning mechanism; a first storage unit configured to store aturning angle neutral point correction value being a difference betweena median of the turning angles at respective limits in a right steeringand a left steering and the turning angle when a vehicle is travelingstraight; a second storage unit configured to store an actuator initialposition being a position of a movable portion of the actuator when thevehicle is traveling straight; an actuator position detecting unitconfigured to detect the position of the movable portion of the actuatoras a first actuator position; a first turning angle calculating unitconfigured to calculate, as a first turning angle, the turning angle ofthe wheel turning mechanism with respect to the median of the turningangles at the respective limits in the right steering and the leftsteering on a basis of the first actuator position; and a second turningangle calculating unit configured to calculate a second turning anglewith respect to the turning angle of the wheel turning mechanism whenthe vehicle is traveling straight on a basis of the first actuatorposition, the turning angle neutral point correction value, the actuatorinitial position, and the first turning angle.
 2. The turning angledetecting device according to claim 1, wherein the second turning anglecalculating unit calculates a second actuator position being a positionof the actuator with respect to the actuator initial position on a basisof the first actuator position and the actuator initial position, andcalculates the second turning angle on a basis of a third turning angleobtained by correcting the first turning angle by the turning angleneutral point correction value and the second actuator position.
 3. Theturning angle detecting device according to claim 2, wherein the secondturning angle calculating unit calculates an actuator positiondifference being a difference between a third actuator positioncorresponding to the third turning angle and the second actuatorposition, and corrects the third turning angle on a basis of a productof a ratio of an amount of change in the turning angle of the wheelturning mechanism to an amount of change in the position of the movableportion of the actuator and the actuator position difference tocalculate the second turning angle.
 4. The turning angle detectingdevice according to claim 3, wherein the second turning anglecalculating unit calculates the third actuator position by obtaining aremainder of a product of a conversion coefficient being a reciprocal ofa ratio of the amount of change in the turning angle of the wheelturning mechanism to an amount of rotation of a rotation shaft of amotor being the actuator and the third turning angle divided by 360degrees.
 5. The turning angle detecting device according to claim 2,wherein the second turning angle calculating unit calculates, as anactuator position difference, a remainder when a difference of thesecond actuator position subtracted from a product of a conversioncoefficient being a reciprocal of a ratio of an amount of change in theturning angle of the wheel turning mechanism to an amount of rotation ofa rotation shaft of a motor being the actuator and the third turningangle is divided by 360 degrees, and corrects the third turning angle ona basis of a value of the actuator position difference divided by theconversion coefficient to calculate the second turning angle.
 6. Theturning angle detecting device according to claim 2, comprising a thirdstorage unit configured to store a correction amount difference being adifference between a product of a conversion coefficient being areciprocal of a ratio of an amount of change in the turning angle of thewheel turning mechanism to an amount of rotation of a rotation shaft ofa motor being the actuator and the turning angle neutral pointcorrection value and the actuator initial position, wherein the secondturning angle calculating unit calculates, as an actuator positiondifference, a remainder obtained by dividing a difference of thecorrection amount difference and the first actuator position subtractedfrom a product of the first turning angle and the conversion coefficientby 360 degrees, and corrects the third turning angle on a basis of avalue of the actuator position difference divided by the conversioncoefficient to calculate the second turning angle.
 7. The turning angledetecting device according to claim 2, wherein the second turning anglecalculating unit corrects the third turning angle on a basis of adifference of a product of a ratio of an amount of change in the turningangle of the wheel turning mechanism to an amount of change in theposition of the movable portion of the actuator and the second actuatorposition subtracted from the third turning angle to calculate the secondturning angle.
 8. An electric power steering device comprising theturning angle detecting device according to claim 1, wherein theactuator is driven on a basis of the second turning angle to apply aturning assist force to the wheel turning mechanism.